Black and white rhinoceros (Diceros bicornis and Ceratotherium simum) are iconic African species that are classified by the International Union for the Conservation of Nature (IUCN) as Critically Endangered and Near Threatened (http://www.iucnredlist.org/), respectively [1]. At the end of the 19 century, Southern white rhinoceros (Ceratotherium simum simum) numbers had declined to fewer than 50 animals in the Hluhluwe-iMfolozi region of the KwaZulu-Natal (KZN) province of South Africa, mainly due to uncontrolled hunting [2,3]. Efforts by the Natal Parks Board facilitated an increase in population to over 20,000 in 2015 through aggressive conservation management [2]. Black rhinoceros (Diceros bicornis) populations declined from several hundred thousand in the early 19 century to ∼65,000 in 1970 and to ∼2,400 by 1995 [1] with subsequent genetic reduction, also due to hunting, land clearances and later poaching [4]. In South Africa, rhinoceros poaching incidents have increased from 13 in 2007 to 1,215 in 2014 [1]. This has occurred despite strict trade bans on rhinoceros products and strict enforcement in recent years.

Thirty protein-coding loci of southern African black rhinoceros (Diceros bicornis) from four isolated populations were studied using starch gel electrophoresis and polyacrylamide gel electrophoresis. Gene diversity estimates varied between 0.036 and 0.058, with the Zambezi Valley population having the largest amount of protein variation. These levels are higher than those in other studies of genetic variation in black rhinoceros and are similar to the amount of genetic variation observed for outbred natural populations that are not genetically depauperate. Because the observed levels of genetic variation vastly exceed the expectations for current effective population sizes, the current levels apparently reflect large black rhinoceros populations which have existed until recently. Observed levels of genetic variation within populations are consistent with the expectations when recent demographic events are taken into account.

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Despite an on-going struggle to conserve the endangered black rhinoceros (Diceros bicornis) since the 1980s, huge capital investment and several genetic surveys, the level of genetic structure and connectivity among populations in southern Africa is not well understood. Here, we undertake a major population genetic study of black rhinoceros in the Zimbabwe Lowveld, an area inhabited by over half of that country's original Zambezi descendants plus one large population sourced from the relict KwaZulu stock of South Africa. Using nuclear microsatellite and mitochondrial DNA data, we found much higher levels of genetic diversity in the indigenous Zimbabwean populations, where observed multilocus heterozygosity was 0.54 versus 0.40 in KwaZulu, and maternal haplotype diversity was 0.77 versus 0.03. We show, for the first time, that both gene pools can be differentiated from each other on the basis of nuclear markers. This, along with the discovery of recent gene flow between all Lowveld populations, suggests that Zimbabwean and South African gene pools were prehistorically connected.

Alibhai and Jewell (this issue) list what they regard as five contra-indications to routine radio-collaring; their list can be used as a basis for presenting alternative perspectives that stem from the radio-collaring experience in Zimbabwe. Their first point concerns the financial expenditure associated with radio-collaring. Alibhai and Jewell do not present any information to support their conclusion that radio-telemetry of rhinos is financially impractical in developing countries. Radio-telemetry is certainly expensive, but so are many other essential aspects of rhino management and protection, and major donor support is often required to effectively protect rhinos in range states such as Zimbabwe. So, accepting that radiocollaring is costly, we have to go on to ask whether it is nonetheless cost-effective as a tool for rhino monitoring in certain circumstances. In Zimbabwe, relevant circumstances have arisen in the 'intensive protection zones' (IPZs) at Sinamatella and Matusadona. These large IPZs, each over 1000 sq km, contain relatively small rhino populations (<100 animals), and are unfenced portions of larger protected areas. Manpower resources are insufficient to provide blanket coverage at an 'intensive' level, and manpower therefore has to be deployed in accordance with information on the current distribution of the rhinos. The circumstances in small, fenced areas, or in larger areas with higher rhino densities or with higher manpower levels, would not generally justify routine radio-collaring. If, as is stated by Alibhai and Jewell, the scale of radiocollaring in Zimbabwe is 'unusual' this is simply because of these different circumstances and not because other range states hold fundamentally different views on the circumstances that would justify radiocollaring. Indeed, there is currently a project within the Southern African Development Community (SADC) Rhino Programme (a regional capacity-sharing programme that involves all the southern African range states) to undertake ongoing trials of rhino radio-collars. Raoul du Toit World Wide Fund for Nature,